Model Roundup and Hobbylinc are my go-to online hobby shops. I live in Georgia and they both ship out of Atlanta, so the shipping costs are always palatable. Hobbylinc has a cool rewards point system for discounts and their prices are already pretty low. @Raoul Ross is correct that they seem a little slower at getting the orders out than they used to. Probably understaffed.
Model Roundup has a lot of out-of-production kits but they ain’t cheap. I usually have anything I order from them in my hands within 3 days. i’ve ordered a number of supplies from them. Again, not the lowest prices on the web, but the lightning quick turnaround and A+ service are worth it to me.
I’ll also vouch for Spotlight Hobbies. Nice prices and quick to ship with fair shipping costs.
i’ve only window shopped at Burbank’s, but they do have competitive prices. I imagine if I lived left of the Rockies they’d pocket a lot of my model budget.